Decades ago the only type of car was the internal combustion (gasoline)type. Other varieties have arrived such as Hybrid and electric. With the new choices are other decisions such as which one reduces most the carbon footprint (or is the most green)and which one is the most cost effective. No more is "the miles per gallon" a standard that can be applied across the board as a specification.

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The efficiency of a car will depend, obviously, on the overall weight and size. Consumers will buy vehicles for their perceived needs. The new breeds of cars that are evolving depend on other features to improve performance and efficiency. They fall into the following categories: hybrid, all electric, high efficiency gasoline engines.

A hybrid electric (HEV) is a type of vehicle which combines a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional vehicle, or better performance.

A variety of types of HEV exist, and the degree to which they function as EVs varies as well. The most common form of HEV is the hybrid electric car, although hybrid electric trucks (pickups and tractors) also exist.

Modern HEVs make use of efficiency improving technologies such as regenerative braking, which converts the vehicle's kinetic energy into battery replenishing electric energy, rather than wasting it as heat energy as conventional brakes do. Some varieties of HEVs use their internal combustion engine to generate electricity by spinning an electrical generator (this combination is known as a motor-generator), to either recharge their batteries or to directly power the electric drive motors.

Many HEVs reduce idle emissions by shutting down the ICE at idle and restarting it when needed; this is known as a start-stop system. A hybrid-electric produces less emissions from its ICE than a comparably-sized gasoline car, as an HEV's gasoline engine is usually smaller than a pure fossil-fuel vehicle, and if not used to directly drive the car, can be geared to run at maximum efficiency, further improving fuel economy.

A hybrid car definitely reduces air emissions because of its using sources of energy otherwise wasted in a conventional car engine.

An electric car is an automobile which is propelled by an electric motor which is entirely powered by electrochemical cells. Electric cars are usually powered by on board battery packs, and as such are usually battery electric vehicles, although some are powered by fuel cells.

Although electric cars often give good acceleration and have generally acceptable top speed, the lower specific energy of production batteries available in 2010 compared with fossil fuels means that electric cars have relatively low range between charges, and recharging can take significant lengths of time. For shorter range commuter type journeys, rather than long journeys, electric cars are practical forms of transportation and can be inexpensively recharged overnight. Longer range journey options are currently being pursued as cities such as New York and states such as Washington start building a charging station infrastructure.

Electric cars will not emit as many pollutants as an conventional car engine but the electricity is generated somewhere and at that source the same (though more controlled) air emissions will occur.

There are other factors to consider also such as the relative capital cost of a vehicle and how much it costs per mile to drive. At the moment due to limited production capacities, capital costs are higher than they will be eventually though governmental subsidies help reduce this burden. Also there is limited durability and long term maintenance of the new breeds of cars that is still to be determined by real data.

Hybrid cars, because they still use gasoline, can still be measured in miles per gallon. Hybrids can get 40 -50 miles per gallon as compared to the equivalent gasoline engine performance of 25 to 35. This is about 6 cents per mile for gasoline cost alone for hybrids. A comparable gasoline vehicle would be about 10 cents per mile.

Electric costs for electric cars are variable depending on where you live as well as when you use it (night time rates can be lower to less demand). Others have estimated this cost as around 2 to 4 cents per mile which is comparable to hybrid and gasoline vehicles.